Prior cam type buckles restrain slippage of the strap by pinching the strap between a transverse blade of a pivotable tongue and the floor of a groove formed in a generally flat base of the buckle. In applications which subject the strap to high levels of compression, the base may bow out under the strain exerted by the blade compressing the belt against the floor of the groove. This limits the pinching force attainable, which limits the tension or cinching force which the belt can hold.